Animals with different forms of experimental obesity display different patterns of dietary self-selection when offered separate sources of the three macronutrients, protein, fat and carbohydrate. Two basis questions are raised by this general finding. First, what factors determine differences in selection patterns observed between lean and obese animals and among animals with different forms of obesity. To answer this question the effects of varying the nutrient density of palatability of dietary components on selection patterns are being examined in lean animals and animals made obese by 1) destruction of the ventromedial hypothalamus, 2) microsurgical hypothalamic knife cuts, 3) neonatal administration of monosodium glutamate and 4) removal of the ovaries. The second question raised by our general finding is, do changes in selection patterns serve a beneficial role in ameliorating the deleterious aspects of obesity or do they serve to exacerbate the pathophysiological conditions of obesity. To investigate this issue physiological measures associated with obesity are being compared in animals maintained on a self-selection regime and animals given a single diet containing the macronutrients in the same proportions as those typically chosen by lean animals. An additional goal of this research project is the investigation of the effects of anorectic drugs on self-selection in lean and obese animals.